Air-classification systems for the separation of solid waste materials are well known. Such systems typically separate waste materials according to density and shape in a gross-type separation process, whereby very heavy materials; for example, stones, glass and metals, medium heavy materials like plastics, cardboard and paper and wood and paper products, and very lightweight materials like dirt, dirt particles, light paper, etc. are separated. The mixed material is dropped into a vertically rising or even a zigzag-type column with a rising airflow, whereby gross segregation of heavy, medium and light fractions occurs.
Although such systems often are useful and desirable, the economic value of the systems is limited, since only gross types of segregation occur, and the segregated waste often has limited economic value, while also comprising a mixture of similar-density, but differently composed and valued, material. Vertical air-classification systems, for example, are described in U.S. Pat. Nos. 3,907,670 and 3,986,949, while horizontal air-classification systems are represented by U.S. Pat. No. 1,290,895.
One unique type of solid waste material is mixed office-paper waste generally named for and derived from waste materials from administrative or office operations in comparison to industrial, municipal or household solid waste material. Mixed office waste has a low economic value and limited commercial utility. Typically, the office-paper waste comprises principally printing and writing paper of greater commercial utility, and hence greater value. However, materials in the waste, such as small amounts; for example, up to 15% by weight, such as 2 to 10%, of other low-grade paper-like materials, such as coffee cups, recycled board, corrugated boxes and small amounts of contaminants, mainly carbon paper, plastic film, glassine paper, hot-melt adhesives, etc., diminish substantially the value and utility of the mixed office-waste material. Thus, there exists a need for the efficient, simple and economical segregation of the components of mixed office-paper waste which will permit the recovery of the more economically valuable components therein.